Dipole illumination

ABSTRACT

A system for fabricating patterns on a semiconductor, the system includes a first aperture having two openings aligned in a first axis, a first mask, a second aperture having two openings aligned in a second axis, and a second mask. The system may be implemented with the second axis substantially perpendicular to the first axis.

BACKGROUND

[0001] This description relates to fabricating. semiconductors.

[0002] Patterns may be fabricated on a semiconductor (e.g., a siliconwafer) by transmitting beams of light through a mask and onto a surfaceof the semiconductor. In order to produce patterns with extremely smallpitches (i.e., the distances between lines) on a semiconductor a phaseshifting mask (PSM) may be used. PSMs cause the shifting of the phase ofa light source so that the peaks of one wave of light lines up with thevalleys of an adjacent wave, effectively canceling each other out andproducing a dual-beam image (a “shadow” image) between the waves that issmaller than the two waves themselves. The dual-beam image may be usedto fabricate patterns having pitches as low as one-half the theoreticalminimum pitch of the light source. In the PSM fabrication technique,light source beams are transmitted through zero degrees and 180 degreesand, when passing through the PSM mask, result in cancellation of thezero degree order of the light.

[0003] Fabrication of semiconductor patterns may be achieved byperforming a double-light exposure which refers to a first lightexposure in a lateral axis (e.g., an “x-axis exposure”) followed by asecond light exposure in a second orthogonal axis (e.g., a “y-axisexposure”).

[0004] “Negative” photoresistive materials (“resists”) may be used aspart of a semiconductor patterning process. Negative resists refers tothe property of a resist that becomes insoluble when exposed to a lightbeam, therefore the exposed area of the negative resists remains on thesubstrate after processing of the semiconductor substrate.

DESCRIPTION OF THE DRAWINGS

[0005]FIG. 1 is a diagram of a dipole illumination apparatuscorresponding to a first exposure of a substrate.

[0006]FIG. 2 is a diagram of a dipole illumination apparatuscorresponding to a second exposure for a substrate.

[0007]FIG. 3 is a diagram of a substrate that may be produced using theapparatus of FIGS. 1 and 2.

[0008]FIG. 4 is a flowchart of a process that may be performed using theapparatus of FIGS. 1 and 2.

DESCRIPTION

[0009]FIGS. 1 and 2 depict a dipole illumination system 10 that may beused to form patterns using a double-light exposure on a semiconductorsubstrate 12. System 10 includes a first dipole aperture 20 and a firstmask 25 that are used for forming x-axis features on substrate 12(during a first exposure 14 of substrate 12, see FIG. 1), and a seconddipole aperture 30 and a second mask 35 that are used for forming y-axisfeatures (during a second exposure 16 of substrate 12, see FIG. 2). Inmore detail, first mask 25 includes openings 26 that allow the passingof spatial frequencies in a lateral (x-axis) direction, and firstaperture 20 includes a first set of dipole openings 20 a and 20 b thatdiffract light source beams 9 in the x-axis. As will be explained,dipole opening 20 b causes the 0^(th) and +1 order of light in thex-axis to be “collected” (e.g., combined) on the pupil of lens 18, anddipole opening 20 a causes the 0^(th) and −1 order of light in thex-axis to be collected on the pupil of lens 18. Similarly, second mask35 includes openings 36 to allow the passing of spatial frequencies in alongitudinal (y-axis) direction, and second aperture 30 includes asecond set of dipole openings 30 a-30b that diffract light source beams9 in the y-axis onto lens 18. Dipole opening 30 b causes the 0^(th) and+1 order of light in the y-axis to be collected on the pupil of lens 18,and dipole opening 30 a causes the 0^(th) and −1 order of light in they-axis to be collected on the pupil of lens 18. The smaller the pitchbetween features (e.g., openings) in masks 25 and/or 35, the smaller theintensity of the diffracted ±1 orders of light passed through thosefeatures from apertures 20 and/or 30, respectively. Therefore, atrelatively small pitches the decreased intensity of the diffracted ±1orders of light at the center of the lens 18 is similar to that createdusing a PSM where the 0^(th) order light at the center of the lens iseffectively cancelled.

[0010]FIG. 1 includes top-down views 40 and 42 that depict thedistribution of diffracted light onto the top 19 of lens 18 afterpassing through dipole openings 20 b and 20 a, respectively. In bothtop-down views 40 and 42, the diffracted beam patterns include a 0^(th)order light 40 b, and ±1 light 40 a and 40 c. As shown in top-down view40, the diffraction of light beam 9 through first dipole opening 20 bcauses the x-axis −1 light 40 a to be shifted off lens 18, the 0^(th)order light 40 b to be shifted to an edge of the entrance pupil of lens18, and x-axis +1 light 40 c to be shifted onto the top 19 of lens 18(and passed through lens 18 to substrate 12). Referring to top-down view42, the diffraction of light beam 9 through mask 25 by second dipoleopening 20 a causes the x-axis +1 light 40 c to be shifted off lens 18,0^(th) order light 40 b to be shifted to an edge of lens 18, and thex-axis −1 light 40 a to be shifted onto the top 19 of lens 18 (andpassed through lens 18 to substrate 12).

[0011] Similarly, FIG. 2 includes top-down views 50 and 52 that depictthe distribution of diffracted light onto the top 19 of lens 18 afterpassing through dipole openings 30 b and 30 a, respectively. In bothtop-down views 50 and 52, the diffracted beam patterns include a 0^(th)order light 50 b, and ±1 light 50 a and 50 c. Referring to top-down view50, the diffraction of light beam 9 through first dipole opening 30 bcauses the y-axis −1 light 50 a to be shifted off the lens 18, the0^(th) order light 50 b to be shifted to an edge of the entrance pupilof lens 18, and x-axis +1 light 50 c to be shifted onto the top 19 oflens 18 (and passed through lens 18). Similarly, as shown in top-downview 52, the diffraction of light beam 9 through second dipole opening30 a causes the y-axis −1 light 50 c to be shifted off the lens 18, the0^(th) order light 50b to be shifted to an edge of lens 18, and they-axis +1 light 50 c to be passed onto the top 19 of lens 18.

[0012] Masks 25 and 35 are examples of so-called binary masks, e.g.,masks arranged to have spatial frequencies in a single direction, oraxis. Binary masks are relatively simple to fabricate and inspect fordefects as compared to phase-shift masks (PSMs), and in particular, ascompared to chromeless PSMs. Therefore, the use of system 10 tofabricate patterns on a semiconductor may be performed using relativelysimple binary masks.

[0013] In an embodiment, the resolution (e.g., the “pitch” ) of linepatterns formed on a semiconductor depends, in part, on the locationand/or the diameter of the dipole opening on an aperture. For example,the further apart dipole openings 20 a-20 b are located from the center22 of aperture 20 the smaller the pitch of system 10. The diameter andlocations from the center line of the dipole openings may be expressedin terms of σ_(c), which refers to units of partial coherence (i.e.,Numerical Aperture Condenser/Numerical Aperture Imaging). In anembodiment, σ_(c) is within a range 0 to 1, inclusive.

[0014] In an embodiment, pitch is defined by the equation:

pitch=λ/(2 NA×σ_(c)), where λ=wavelength.

[0015] Therefore, using an exemplary light source beam wavelength of 193nm, 0.6 NA and with dipole openings of 0.05 σ_(c), located at atσ_(c)=0.95, the minimum pitch would equal approximately 170 nm. Or, asanother example, using a light source beam wavelength of 193 nm stepperwith 0.75 NA, and with openings of 0.05 σ_(c), located at σ_(c)=0.95,the minimum pitch would equal approximately 135 nm.

[0016]FIG. 3 shows a pattern that may be formed on a negative resistcoating 55 on a surface 56 of substrate 12 using system 10. As describedherein, negative resists may be used to create patterns on a substrate,e.g., where the light exposure on the negative resist causes the exposedarea to become insoluble and remain after processing of the substrate.In this example, first exposure 14 (using aperture 20 and mask 25)causes line/space pattern 50 to be formed on substrate 12, and secondexposure 16 (using aperture 30 and mask 35) causes line/space pattern 60to be formed on substrate 12. Pattern 70 represents a combined patternof patterns 50 and 60, which leaves voids 75 a-75 n between the exposedpatterns 50 and 60.

[0017] In an embodiment, voids 75 a-75 n expose areas in a lower layerof substrate 12, i.e., a lower layer beneath negative resist coating 55.In an embodiment, voids 75 a-75 n expose areas usable as electricalcontacts in the lower layer, e.g., the contacts may be useful in thefabrication of a semiconductor device, such as a semiconductor memorydevice.

[0018]FIG. 4 depicts a flowchart of process 100 that may be used to forma pattern on a semiconductor. Process 100 includes transmitting (110) alight source beam through a first dipole aperture and a first mask in afirst axis onto a semiconductor, and transmitting (120) a light sourcebeam through a second dipole aperture and a second mask in a second axisonto the semiconductor to form a pattern on the semiconductor. Process100 may optionally include forming a pattern on a negative resist layeron the semiconductor (not shown).

[0019] The invention is not limited to the specific embodimentsdescribed above. For example, some embodiments described the formationof a pattern that included contact “holes” that are essentially round inshape. However, other pattern geometries may be formed using the dipoleillumination apparatus using different shapes and patterns formed on themask(s).

[0020] Other embodiments not described herein are also within the scopeof the following claims.

What is claimed is:
 1. A system for fabricating patterns on asemiconductor, the system comprising: a first aperture having twoopenings aligned in a first axis; a first mask; a second aperture havingtwo openings aligned in a second axis: and a second mask.
 2. The systemof claim 1, wherein the second axis is substantially perpendicular tothe first axis.
 3. The system of claim 1, wherein the first maskincludes openings aligned with the first axis and operative to formfeatures in the first axis on the substrate, and wherein the second maskincludes openings aligned with the second axis and operative to formfeatures in the second axis on the substrate.
 4. The system of claim 1wherein at least one of the first and second mask comprise a binarymask.
 5. The system of claim 1, wherein at least one of the first andsecond mask comprises a phase shift mask.
 6. The system of claim 1,wherein a diameter of the two openings of first and second apertures aresubstantially equal and the distance between the two openings is greaterthan zero but less than or equal to two times the diameter.
 7. Thesystem of claim 1, further comprises: a light source; and a substratehaving at least one layer of photoresistive material sensitive to thepassing of light through at least one of the first mask and firstaperture, and the second mask and second aperture.
 8. The system ofclaim 7, wherein the photoresistive material comprises a negativephotoresistive material.
 9. A method of forming a pattern on asemiconductor comprising: transmitting light through a first aperturehaving at least two openings aligned in a first axis; transmitting thelight from the first aperture through a first mask onto a semiconductorsubstrate; transmitting light through a second aperture having at leasttwo openings aligned in a second axis; and transmitting light from thesecond aperture through a second mask onto the semiconductor substrate.10. The method of claim 9, wherein the second axis is substantiallyperpendicular to the first axis.
 11. The method of claim 9, whereintransmitting light through the first mask comprises transmitting lightthrough the first mask having openings aligned with the first axis andoperative to form features in the first axis on the substrate, andwherein transmitting light through the second mask comprisestransmitting light through the second mask having openings aligned withthe second axis and operative to form features in the second axis on thesubstrate.
 12. The method of claim 9, wherein at least one of the firstand second mask comprises a binary mask.
 13. The method of claim 9,wherein at least one of the first and second mask comprises a phaseshift mask.
 14. The method of claim 9, wherein a diameter of the twoopenings of first and second apertures are substantially equal and thedistance between the two openings is greater than zero but less than orequal to two times the diameter.
 15. The method of claim 9, furthercomprises: transmitting the light trough the first and second maks ontoa substrate having at least one layer of photoresistive materialsensitive to the passing of light through at least one of the first maskand first aperture, and the second mask and second aperture.
 16. Themethod of claim 15, wherein the photoresistive material comprises anegative photoresistive material.
 17. An apparatus comprising: a firstaperture having two openings aligned in a first axis; a first mask; asecond aperture having two openings aligned in a second axis; and asecond mask.
 18. The apparatus of claim 17, wherein the second axis issubstantially perpendicular to the first axis.
 19. The apparatus ofclaim 17, wherein the first mask includes openings aligned with thefirst axis and operative to form features in the first axis on thesubstrate, and wherein the second mask includes openings aligned withthe second axis and operative to form features in the second axis on thesubstrate.
 20. The apparatus of claim 17 wherein at least one of thefirst and second mask comprise a binary mask.
 21. The apparatus of claim17, wherein at least one of the first and second mask comprises a phaseshift mask.
 22. The apparatus of claim 17, wherein a diameter of the twoopenings of first and second apertures are substantially equal and thedistance between the two openings of is greater than zero but less thanor equal to two times the diameter.
 23. The apparatus of claim 17,further comprises: a light source; and a substrate having at least onelayer of photoresistive material sensitive to the passing of lightthrough at least one of the first mask and first aperture, and thesecond mask and second aperture.
 24. The apparatus of claim 23, whereinthe photoresistive material comprises a negative photoresistivematerial.